1. Field of the Invention
The present invention pertains to a method for making a multitrack head, and to a multitrack head.
A combined technology is generally used for making multitrack heads: massive technology for the magnetic circuit and the windings, and thin-layer technology for the poles. The magnetic circuit is made of ferrite and has a base plate from which there protrude pads separated by grooves and arranged in a regular network. The poles are made of magnetic material and formed on the pads by connecting the pads diagonally over the space between the pads, with a narrow gap (generally smaller than one micron) being made in the middle of these poles. Thus, a dense network of magnetic micro-heads is obtained.
2. Description of the Prior Art
There are several known methods for the manufacturing of such magnetic heads. The ferrite magnetic substrate may be made by mechanical grooving of a substrate, the filling of the grooves with a non-magnetic material such as glass, and polishing of the upper face of the filled substrate. The network of poles can then be deposited on this polished face. This deposit can be made according to the thin-layer tehnique, with polishing steps (see for example the French patent application No. 86 14974).
The control wires for the network of magnetic heads can be embedded in the glass that fills the grooves made in the substrate. Such a method has drawbacks: the conductive wire embedded in the glass should have an expansion coefficient close to that of glass and ferrite. This rules out the use of copper. The high temperatures (greater than 600.degree. C.) needed for the melting of the glass rule out the use of insulated wires, and this makes it difficult to fabricate wound matrix heads. The mechanical grooving, done with a standard mill, produces rectangular-sectioned grooves whereas the search for improved efficiency of the magnetic heads would lead to the narrowing of these grooves at the poles. And the presence of wires going out of the substrate is very much of an inconvenience during the formation of the poles by the thin-layer technique.
There are methods, known from the French patent applications Nos. 87 14 820 and 87 148 24, for making magnetic heads According to these methods, V-shaped grooves are made in the ferrite substrate, and they are partially filled with glass. This removes a part of the above-mentioned drawbacks through the narrowing of the grooves in the vicinity of the poles and through the fact that a free space is left in the grooves, making it possible to do the winding at a final stage. However, it is difficult to implement these methods because the first polishing has to be done with very high precision for the width of the grooves, which is a vital parameter of the magnetic heads, greatly depends on it. Furthermore, it is difficult, if not impossible, to check the partial filling of the grooves, especially in the case of multitrack heads.